One long-used method of improving tyre grip in wet-road and winter conditions is to form a porous surface on the tread. The pores increase the tread-road contact area, as well as allowing run-off of the water layer that forms between the tread and the road surface.
To obtain a porous-surface tread, the common practice in the rubber industry is to add to the compound, as it is being made, specific chemical agents which, at the curing stage, produce chemical reactions releasing pore-forming gases.
This solution has both cost and processing drawbacks, the former because of the chemical agents added to the compound, and the latter by having to constantly control the temperature of the compound as it is processed, to prevent the chemical agents from reacting prior to the curing stage.
A need is therefore felt for a method of producing a tread with a given porosity, while at the same time avoiding the drawbacks of the known art.
The Applicant has surprisingly discovered that using given amounts of recycled rubber in the form of granules of given size produces tyre treads with the required degree of porosity, but without incurring the drawbacks of the known art.
More specifically, the Applicant has devised a method of producing tread portions capable of acquiring the required surface porosity in actual use.
One of the original aspects of the present invention, in fact, lies in obtaining a tread of given porosity using a completely different strategy from that adopted so far. That is, as opposed to producing a tread portion with the required winter-tyre porosity from the outset, the present invention provides for producing a tread portion that achieves the required porosity with actual use, thus eliminating the use of chemical agents for producing pores at the curing stage.